1. Field of the Invention
The present invention relates to a forming method of a glass product such as a panel for a cathode ray tube (CRT) wherein a lump of glass (gob) in a molten state is dropped from an orifice (feeding port) to a female press-mold which is pressed by a male press-mold (plunger), and its device, particularly to a novel forming method of a glass product and its device with respect to a line wherein the female press-molds are successively set at a gob feeding stage, the gob is continuously fed and a glass product is successively removed after subjecting the gob to a press-forming step.
Conventionally, a method has normally been adopted in case of press-forming a glass product such as a panel for a CRT, wherein female press-molds are placed along a periphery of a rotatable disk-like table, gob is successively fed to the female press-molds placed on the table by dropping the gob from an orifice provided above the rotating table, the female press-molds are successively transfered to a press-forming stage and a glass product is press-formed by pressing the gob by a plunger.
In such a forming method of a glass product, the female press-molds are successively set at a single gob feeding stage, the gob is continuously fed, the female press-molds fed with the gob are successively transferred to the press-forming stage and the press-forming step is performed. Accordingly, the timing for feeding the gob is normally determined inevitably by a sum of a pressing time and a transfer time (index time) which is required for transferring the female press-mold from a gob feeding stage to the press-forming stage. For instance, when the pressing time is approximately 3 seconds and the index time is approximately 2 seconds, the timings of feeding the gob are at intervals of approximately 5 seconds, and therefore, the molding rate of a glass product is restricted to approximately 12 pieces per minute. Therefore, there has been a request for further promoting the molding efficiency of a glass product.
As a conventional molding method of a glass product wherein the molding efficiency of a glass product is promoted in response to the request, there is a method (Japanese Examined Patent Publication No. 23421/1989), wherein, for instance, as shown in FIG. 50, female press-molds M on a disk-like turn table T are successively set with respect to a single gob feeding stage S1 (1 in FIG. 50) to which gob is continuously fed by a gob feeding device G, the female press-molds M which are set with respect to the gob feeding stage S1 are transferred by every pitch (m), and at a stage wherein the female press-molds M fed with the gob are transferred to continuous press-forming stages S21 and S22 (4 and 5 in FIG. 50), the press-forming step is simultaneously carried out by a press device P. Or, there is a method (see Japanese Examined Patent Publication No. 44648/1989), wherein as shown in FIG. 51, the female press-molds M on a disk-like turn table T are successively set with respect to gob feeding stages S11 and S12 (1 and 2 in FIG. 51), the female press-molds M which are set in the gob feeding stages S11 and S12 are transferred by every two pitches (2 m), and at the stage wherein the female press-molds M fed with the gob are transferred to two contiguous press-forming stages S21 and S22 (3 and 4 in FIG. 51), the press-forming step is simultaneously carried out by the press device P.
In the former type of device, although it is certainly possible to accelerate the timing for feeding the gob at the gob feeding stage S1, the time from when the gob touches the female press-mold M to when the pressing step is started, differs between the respective press-forming stages S21 and S22. Accordingly, the moldabilities of glass products respectively molded by the press stages S21 and S22 are different with each other, which is apt to deteriorate the uniformity of the quality of the glass product.
On the other hand, even in case of the latter type of device, although it is certainly possible to accelerate the timing for feeding the gob, by the plurality of the gob feeding stages S11 and S12, the gob which is fed to the female press-molds at the respective gob feeding stages S11 and S12 are dropped from different orifices. Accordingly, a variation is apt to cause inherently in the size of the gob, the moldabilities of the glass products respectively molded by the press-forming stages S21 and S22 differ from each other by the variation, and the uniformity of the quality of the glass product is apt to deteriorate.
Further, in both the former and the latter type of devices, heat is radiated from the female press-molds M when the gob is fed to the female press-molds M. The female press-molds M are placed in the vicinity of the outer periphery of the turn table T along its peripheral direction. Therefore, the rate of heat radiation from the female press-molds M is apt to be nonuniform in the radial direction of the turn table T. Accordingly, the thermal distortion of the female press-mold M is nonuniform in the radial direction of the turn table T, and the dimensions of the glass product are apt to be deviated in the radial direction of the turn table T.
Further, in molding a glass product, it is necessary to provide a gob feeding step, a press-forming step, a glass product removing step, a shell mold attaching step which maintains a mold forming shape by engaging a shell mold to a periphery of a bottom mold in the press-forming step, which is necessary for enabling the press-forming step by the female press-molds M, and a shell mold removing step for removing the shell mold from the bottom mold before removing the glass product which is necessary for enabling the glass product removing step. Since the female press-molds M are placed and transferred on the turn table T, the above respective steps should be laid out on a circular locus of the turn table T which is the transfer locus of the female press-molds M, the number of the female press-molds M or the bottom molds placed on the turn table T is uniquely determined by the size of the turn table T, and it is difficult to arbitrarily increase the number of the female press-molds M or the bottom molds in accordance with the necessity. Therefore, the degrees of freedom in the design of the layout of the molding line of a glass product, and in the alteration in the layout are considerably restricted.